In some application, it may be desirable to accurately determine average output current of an inductor-based DC-DC converter in order to use this information to either limit the output current to a safe level or to disable the converter to preserve battery life when a certain output current level is reached.
For example, in USB-ON-THE-GO applications, a portable converter may supply a regulated 5V boosted voltage to an external connector using a lower voltage Li-Ion battery. Since the output of the converter is exposed, via the connector, to an influence of an external device, the converter may experience fault conditions, such as a short circuit to ground. Therefore, it may be necessary to limit the output current of such a converter or to disable it for preserving battery life.
Furthermore, it would be desirable to measure the average output current fairly accurately so that a converter can always deliver a minimum required current but not a current produced at a level significantly higher than necessary due to a less accurate current measuring technique. For example, a converter may be required to deliver a 500 mA minimum amount of current required by the USB-ON-THE-GO specification.
Moreover, in accordance with a conventional technique, output current may be directly sensed using a current sensing resistor. However, a conventional current sensing resistor has a very large size. Therefore, it occupies substantial space on a circuit board increasing the cost of a converter and causing significant power loss. Accordingly, it would be desirable to determine the output current without the use of a current sensing resistor.